Step-by-step motor



2 Sheets-Sheet 1 A. G. THOMAS STEP-BY-STEP MOTOR INVENTOR.

April s 195s Original Filed Jan. 28, 1954 April 8, 1958 A. G. THOMASsTEP-BY-STEP MOTOR 2 Sheets-Shee 2 Original Filed Jan. 28. 1954 Fly. E

WLM/ INVENTOR.

United States Patent C STEP-BY-STEP MOTOR Albert G. Thomas, Butler, Pa.

Original application January 28, 1954, Serial No. 466,746, now PatentNo. 2,782,354, dated February 19, 1957. Divided and this applicationDecember 31, 1956, Serial No. 627,902

20 Claims.' (Cl. sis- 46) This invention relates to motors andespecially to step motors designed to rotate in predetermined steps orthrough definite displacements. This application is a division from myco-pending application, Serial Number 406,740, filed January 28, 1954,now Patent No. 2,782,- 354, dated February 19, 1957.

In many industrial, military, and other applications it is frequentlydesired to move objects through definite displacements or to rotateshafts through definite angles, in either forward or reverse direction.Typical illustrations are in synchronized pointing of guns, control ofguided missiles, telemetering, automatic control of milling machines,and other machine tools from information on a tape or other record,operation of valves or other control devices at a distance, and variousother uses. Outstanding advantages of this motor are that it can respondstep by step to phased current applied to its wind- Another object isltoprovide a motor with a power 5 booster which can be used to improveacceleration and operating speed of the motor.

A further object is to` provide a motor which will produce relativelygreat power for its size.

An additional object is the provision of an improved brake to preventrotor oscillations.

Another object is to provide a step motor with means for automaticallyapplying a relativelyv heavy starting current at the beginning of eachstep rotor mvement and for automatically reducing the current for theremainder of the step movement.

Other objects will appear in the following description.

In the drawings:

Figure l is a part sectional front elevation of my improved step motorand associated control mechanism.

Figure 2 is a left end view of the motor shown in Figure l.

Figure 3 is an end view of the motor, looking from the right in Figurel, and showing details of a commutator.

In Figure l, the motor has end plates 1 and 2 screwed to base 3 andstator field rings 4, 5, and 6 are separated from the end plates andfrom each other by collars 7. Bolts 8 are passed through bores in thefield rings and collars and clamp them tightly together by means ofsuitable threaded nuts. Dowel pins 9 may be inserted between the collarsand rings to prevent `circumferential shift. Each field `ring has tworows of radial teeth like 10 and 11 of the first section, the inner tipsof which are of equal circumferential width and are equally spaced. Thecircumferential width of these teeth or poles is lreferably equal to thecircular widths of air gaps belice tween them. The stator rings andintegral poles or teeth may be cast of a suitable magnetic metal likemild steel, or they can be assembled from laminations or powdered iron-or steel. It is preferable that the magnetic flux does not have tocross lamination interfaces. The two circular rows of teeth 10 and 11 ofthe first phase are separated by air space 12.

Likewise, poles 13 and 14 are integral with ring 5 of the second phaseand are constructed and spaced similarly to poles 10 and 11. Poles 15and 16, integral with ring 6 of the third phase, are constructed andspaced in like manner to that described. The teeth or poles of the threephases are preferably in line, looking at the motor endwise, but this isnot essential. The teeth 11, 14, and 16 may be offset from teeth 10, 13,and 15, to provide more space for windings, or for other reasons.

The rotor is made of three sections or phases comprising cylindricalcores 17, 18, and 19, spaced by collars 20 and 21 which are fastened toshaft 22 by set screws. Suitable through bolts 23 clamp the rotorsections and collars 20 and 21 tightly together into a unitarystructure. Holes 24, 25, and 26 are cast or bored in the rotor to makeit relatively light in weight. Rotor section 17 has radial teeth orpoles 27and 28 angularly and axially spaced to bring the tips of theseteeth into register with the tips of the teeth 1I) and 11. Thecircumferential width of the rotor teeth for all three phases islikewise equal to the spacing between the teeth. Assuming that rotorteeth 27 and 28 are in register with associated stator teeth 10 and 11,respectively, the rotor teeth 29 and 30 are positioned so that theyoverlapthe respective stator teeth 13 and 14 by 1/3 tooth width.Likewise, when rotor teeth 29 and 30 are in register with associatedstator teeth 13 and 14, the rotor teeth 31 and 32 of the third phaseoverlap the associated stator teeth 15 and 16 by 1/sy tooth width.

The rotor sections or phases can be made of cast mild steel orl may befabricated of laminations or of powdered iron. The air gap between thestator and rotor is preferably small, on the order of 0.005 inch orless. The shaft 22 is rotatable in vbearings 27a and 28a fastened inrespective end plates 1 and 2. These bearings can be of the ball 0rroller type, if desired. Spacing collars 29a and 30a are fastened toshaft 22 by set screws and carry attached annular rings 31a and 32a,respectively, of insulating material such -as Bakelite or the like.Brass or other slip rings 33 and 34 are fastened in insulating element31a, and similar slip rings 35 and 36 are fastened in insulating element32. Slotted insulating block 37 is fastened to the inner face of plate 1and has spring-pressed brush 38 slidable in a slot and in contact withslip ring 33. Similar block 39 is fastened to plate 1 and carries brush40 in contact with slip ring 34. Slip rings 33 and 34 are electricallyconnected with the ends of toroidal magnetizing winding 41 wound aroundrotor element 17 and situated in the space between teeth 27 and teeth28.

Insulating block 42 is likewise slotted to hold springpressed brush 43and is screwed or otherwise fastened to teeth 14, although it can befastened to any fixed part of the motor. This brush is in contact withslip ring 44 which is rotated by attached ring 45 of suitable insulatingmaterial. This ring is pressed on or screwed to collar or spacer 21 androtates therewith. Slip ring 46 is also carried by insulating ring 45,and brush 47, slidably held in a slot in insulating block 48, is incontact with slip ring 46. Block 48 is attached to some of the teeth 14,or otherwise. Toroidal magnetizing winding 49 is placed around rotorelement 18 and has its ends connected to slip rings 44 and 46. Similarmagnetizing winding 50 is wound around rotor element 19,-with thewinding ends connected to slip rings 35 and 36. Brush 51 is slidable ininsulating block 52 :attached to plate 2 l J and is in contact with slipring 35. Similarly, brush 53 is slidable in insulating block 54 attachedto plate 2. This brush is in contact with slip ring 36.v

The poles or teeth are wound with suitable insulated wire, forming aplurality of connected windings 55 which, when energized, cause all theteeth 10 to be magnetized with, say, north poles at the tips. Therefore,the tips of adjacent rotor` poles 27 will have induced south poles, andthe tips of teeth or poles 28 will have north poles, causing inducedsouth poles inthe tips of adjacent stator teeth 11. The magneticfluxpaths are indicated by the arrows. Rotor winding 41 is connected incircuit with stator winding 55, in series, parallel, or series parallel,as desired. The polarity of winding 4i is arranged, however, to aid themagnetizing effect -of winding 55. Winding 5S is vrconnected to windingL11 through brushes 38 and 40 and -associated slip. rings 33 and 34.This spool-like-rotor winding produces a power- ,ful magnetizing forceand relatively short magnetic .path and, in conjunction with statorwindings, furnishes strong magnetization of the poles with moderate mag-`netizing currents.

The second and third phases are similarly wound, field winding 55b ofthe second section `or phase being electrically connected with rotorwinding 49 through brushes 43 and 47 and associated slip rings. Asbefore, the magnetizing effects of the two windings are arranged to add.Similarly, stator winding 55e of the third section or phase iselectrically connected with rotor winding 50 by means of brushes 51 and53 and associated slip rings. Again, the magnetizing effects of the twowindings add. If desired, shaft 22 may comprise a tube, and theconnections for the rotor windings may be brought through the shaft toslip rings placed on the shaft outl side the casing. f

Cam element 56, having inclined working surfaces arranged in an invertedV, isl bolted 'to plate 1 as shown in Figure 2, and in Figure l. Arm 57is pivoted on stub shaft 58, a reducedend of which.,passes through ahole in plate 1 and is held by nut 59. Similar arm 60 is also Pivoted onthis shaft which rotatably supports hardened metal disc 61 andconcentricfattached pinion 62. Shaft 58 has flange-like head 63 to holdthe arms and disc in axial position. Gear 64, of considerably largerdiameter than the pinion, is keyed to principal shaft 22 'and is meshedwith pinion 62. Commutator 65 (Figure 3) comprises a disc, with hub, ofBakelite or other insulating material, with preferably rectangularcopper or other metal. bars 66 molded in or insertedin slots.or-.holesinnthe commutator disc. Thesebars are electrically connectedwith metal slip ring 68 fastened over the insulating hub of theconimutator. There are the same numberof `equally spaced bars 66 asthere are stepsl in the motor; This number will be three times'thenumber of poles 10. If desired, the number of commutator bars can bereduced and the commutator can be driven by an attached pinion in meshwith gear 64. Proper relationship between the number of steps, bars, andgear ratio should be maintained. The insulating central portion of thecommutator is fastened to shaft 22 by means of set screws or by keying.t

Member 69 is made of Bakelite or other insulating material and has acurvature concentric with shaft 22. This member has slot 70, alsoconcentric with shaft 22 and is guided by screws 71 threaded into holesin plate 2. Arm 69a is integral with `member 69 and supports, by meansof attached screws 73, slotted triangular metal or other .conductivebrush 72 forsliding action toward or away from the axis of shaft22.VKnurled button 74 has an integral reduced shankrotatable in abore inmember 69, being held in place byas'houlder and collar attached to theshank which",- beyond the collar, is threaded and is screwed intoathreaded hole in brush 72.. This brush is arranged to rubv against theyadjacent face of the commutator so that the ends of the rotatingcommutator bars 66 will make contact with the brush for periods of timeincreasing as the brush is moved toward shaft 22 by turning button 74.Similarly, moving the brush in opposite direction will reduce thecontact period. Springs between screw heads 73 and the brush may be usedto urge brush 72 against the ends of the bars.

Boss 75 is integral with plate 2 and has a threaded hole in whichthreaded rod 76, having a knurled head, is screwed. The end of this rodserves as a stop for the contiguous end of element 69 which is pulledagainst this stop by tension spring 77 fastened to element 69 and toboss 75. Therefore, the brush 72 may be shifted along circular pathsconcentric with the axis of shaft 22. The length of time during whichthe brush is in contact with a commutator bar is adjustable by turningbutton 74, since the tapered brush is moved toward or away from shaft22. The phase relationship of the time of contact of a commutator barwith'the brush is determined byY adjusting screw 76 so that -thebrushcontacts are made at definite relative positions of the rotor poles withrespect to the associated stator poles, regardless of which phase orsection of the motor is energized.

Resilient metal strip or other brush 78 is attached to insulating block78a fastened to plate 2 and rubs against slip ring 68 which iselectrically connected with commutator bars 66, but which is insulatedfrom shaft 22.

Circular steel or iron housing element 101 has good magneticpermeability and is attached to shaft 22 in leak-proof manner by meansof a hub and suitable packing. This pan-like housing element has a ange,against which a similar flange of cooperating housing member 104 isforced by screws, a suitable gasket being between the anges. Element 104is also made of good magnetic material and has concentric bearing 105which is rotatable on shaft 106. Packing gland 107 is provided toprevent leakage. Shaft 106 is the shaft of motor 108 which may be of anysuitable type such as shunt or synchronous, for example. Bakelite orother insulating block 109 is attached to motor 108 and carries brushes110 and 111 which are sldable in slots in block 109. Brush 110 ispressed against slip ring 112 by a spring, and brush 111 is `pressedagainst slip ring 113. These slip rings are mounted on an insulatingcollar on shaft 106 and are electrically connected with the ends oftoroidal winding 114 placed around shaft 106 adjacent to attached,concentric magnetizable steel or iron disc 115. This winding is suitablysealed to prevent leakage of liquid to the wires. Shaft 106 has an axialbore, through which conductors connecting the-winding with the sliprings are passed. Packing may be used to protect the bearing fromparticles in the housing.

A mixture of iron particles and oil, iron particles and graphite, or thelike, is contained in housing 10i-104, and occupies space between disc115 and housing 101. Normally, there is little driving action betweendisc 115 and housing 101, but when winding 114 is energized, a magneticflux is developed between the disc and housing, and the disc then iseffectively tightly bound to disc 101. and attached shaft 22. When thewinding 11.4 is de-encrgized, the driving action is largely eliminatedquickly. Current is supplied to winding 114 through conductor 116,connecting brush 111 and positive line 117 through switch 210, and byconductor 118 connected tcnegative line 119 and to brush 7S ofslip ring68 which leads to commutator contacts 66 which in turn periodically makeconnection with brush 72. The remainder ofthe circuit to winding 114 ismade through flexible wire 120 connected to brush 72 and to brush 110.

While this type of clutch is shown, other suitable types of clutchescould be used. The purpose of the clutch is to allow the spinning motor108 to give shaft 22 a quick boost at the beginning of each stepmovement of the step rotor assembly in order to increasepossible speedand hardened roller 81, but which do not limit movement of this rollerin radial direction with respect to shaft 58. This roller is-adapted towedge between hardened surface 82 of element 56 and disc 61 when arm 57is pulled counter-clockwise (Figure 2) by tension spring 84 attached tothe arm and to pin or stud 85 projecting from plate 1. This pinchingaction tightly locks disc 61 against any appreciable mo-vement aboutshaft 58 in counter-clockwise direction, but allows this disc to rotatefreely in opposite direction. Pinion 62 and gear 64 are tightly meshedso that there will be little, if any, back-lash. Therefore, when disc 61is locked against rotation in one direction, gear 64 and attached rotorshaft 22 are locked against rotation in opposite direction.

Solenoid 86 is fastened to plate 1, and its plunger 87 is attached toarm 57 through spring 88 which is considerably stifferV than spring 84.Therefore, when the solenoid is energized, the'plunger is pulled intothe solenoid, and arm 57 is rotated clockwise against the tension ofspring 84 until roller 81 is wedged between hardened surface 83 of brakeelement 56 and disc 61, thereby prohibiting any appreciable rotation ofdisc 61 in clockwise direction, but allowing free rotation of'this discin opposite direction. This, of course, locks the rotor againstcounter-clocl wise rotation, but allows free rotor move-` ment inopposite direction. The surfaces 82 and 83 are symmetrically placed withrespect to disc 61. 1 have found that an angle of 6 between eithersurface and tangents to disc 61, drawn at points of contact of theroller with disc 61, in locking position, will provide goed lock.- ingaction and easy release. The invention is not limited to this angle,however.

Arm 60 is similar to arm 57 and is pivotally supported on shaft 58. Thisarm has attached lugs 89 and 99. similar to lugs 79 and 86, and whichserve to shift roller 91 against hardened cam surface 92 of brake block93 or against hardened cam surface 94 of this block, depending upon thedirection of movement of arm 60. Block 93 is similar to element 56 andis bolted or screwed to plate 1. As with element 56, the braking or camsurfaces approach the disc 61, from the central apex, at such an angleor angles that roller 91 will be wedged against a cam surface and thedisc to prevent rotation thereof in one direction,-

while allowing free rotation in opposite direction.. Tension spring 95is fastened to stud 85 and to arm 6o and normally holds roller 91 incontact with cam surface 92, thereby locking disc 61 against rotation inclockwise direction (Figure 2).

Solenoid 96, similar to solenoid 86, is attachedto plate 1, and itsplunger 97 is connected to arm 60 by means of spring 98, considerablystronger or stiffer than spring 95. Since spring 84 normally causesroller 81 to lock disc 61 against rotation in counter-clockwisedirection, this disc is locked against rotation in either direction whenneither solenoid is energized. Then, energization of solenoid 6 willallow counter-clockwise rotation of disc 61, and energization ofsolenoid 96 will allow clockwise rotation of the disc. lf theself-locking feature, with power off, isnot desired, only one solenoidand locking roller need be used. The end of arm 61) may have notch 99into which locking pawl 100, pivcted to plate 1, may be pressed when itis desired to hold roller 91 in neutral position out of contact witheither cam surface 92 or 94.

Stub shaft 121 is fastened in a hole in end plate 1 andy has flange orcollar 122, Pinion 123 is attached to instilating disc 124 concentrictherewith; and metal disc 125 .gFigure l), having integral slip ring 126concentric with the disc, is attached to the other face of discv 124.Cornmutator bars 127 are smoothly recessed into the periphery of disc124 and are welded or otherwise attached to disc 125. The disc 124 andpinion 123 are axially bored so that they will rotate freely on iiXedstub shaft 121. Cen- .tral holes in slip ring 126 and disc 125 are oflarger diameter than that of shaft 121, to prevent electrical contact.Brush 12S, slidable in insulating block 129 attached to plate 1, isconnected, by means of conductor 130, to the positive terminal of biasbattery or other bias voltage source 131, the negative terminal of whichis connected to the grid of thyratron 132. One end of resistor 133 isalso connected to the positive terminal of bias source 131 and the otherend of this resistor is connected to negative line 119. Conductor 13()leads to switch contact 227 and thence to bias source 131.

Flexible strip-type brush 134 is attached to insulating block 129 and isin contact with slip ring 126. Brush 134 is connected with positive line117 by means of conductor 135. Block 129 has arcuate slot 136 concentricwith shaft 121, and screws 137 are threaded into holes in plate 1. Thesescrews serve as guides for block 129 which may be swung through limitedangles around the axis of shaft 121. The screws may be tightened toclamp the block and brush 128 in any desired position. Brush 134i,through its resiliency, will maintain contact with slip ring 126.Therefore, block 129 and brush 12S can be shifted to vary the timing ofthe contact of this brush with commutator bars 127, the positions ofwhich are dependent upo the position of shaft 22 and attached rotorunits.

The meshing of pinion 123 and gear 64 is close, tov

minimize back-lash. The number of equally spaced coinmutator bars 127 isrelated to the ratio of gears 64 and 123 and to the number of steps ofthe motor in such manner that the commutator assembly 124-127 is rotatedfrom a position of initial contact of a bar 12/ with brush 128 to aposition in which the next succeeding commutator bar'127 makes initialcontact with brush 128 in the same time period as that required for therotor to rotate through one step. The position of the rotor poles orteeth relative to the stator poles or teeth, at the moment of initialcontact of a bar 127 with brush 128, is determined by the position ofbrush 128; and this relative position can be varied by slipping block129 relative to screws 137. In other words, the brush can be adjusted sothat contact with any bar 127 occurs when the rotor teeth overlap thestator teeth by 1/3 tooth width or more or less. This condition is truefor all three phases or sections of the motor, but a separate commutatorfor each phase could be used, if desired. The commutator 124-127 couldbe placed directly on shaft 22 if desired, in which case the number ofbars 127 would be equal to the total number of steps of the motor unlessseparate commutators are used.

One end of stator winding S5 is connected to positive line 117, and thefree end of the connected rotor winding 41 is connected to slip ring 34and thence to brush 40, which is electrically connected to the anode ofthyratron 137 by means of conductor 138. An end of stator winding 55h ofthe second section or phase is likewise connected to line 117,' and theconnected rotor winding terminal is connected to slip ring'46' andthence to the anode of thyratron 139 through `brush 47 and conductor140. Similarly, an end of stator winding 55e of the third motor phase orsection is connected to positive line 117, and the other end of thiswinding is connected to the rotor winding 50 through brush 51 and slipring 35. The other end of this rotor winding is connected to the anodeof thyratron 141 through slip ring 36, brush S3, and conductor 142. Theother brush connections have been described before.

'Condensers 143, 144, and 145 are connected between the anodes ofthyratrons 137-139, 139-141, and 137- 141, respectively. Thesecondensers serve to extinguish any one of these three thyratrons whichis conducting current when any other of the three thyratrons is tired,

The negative poles of bias elements 146,147, and 148 are connected tothe grids-of respective thyratrons'137, 139, and 141. The positive polesof these elements, which may be batteries, rectified voltage supplies orthe like, are connected, respectively, to ends of resistors 149, 150,and 151, the other ends of which are connected to cathode line orconductor 152. The cathodes of these three thyratrons are likewiseconnected to line 152, as shown. The actual values of the capacitors andresistors will vary according to the type of thyratron used andaccording to other factors such as whether photocells, contacts, or thelike, are used to fire the thyratrons.

The grid and cathode connections of thyratron 132 have been described.The anode of this thyratron is connected to one end of resistor 153, theother end of which is connected'to switch 154, which may be closed toconnect the resistor to line 152. The anode of thyratron 155 isconnected to an end of resistor 156, the other end of which is connectedto resistor 153 and a terminal of switch 154. The resistance of element153 is higher than the resistance of element 156 so that thyratron 132will pass less current when tired than will thyratron 155 when itistired. Condenser 157 is connected between the anodes of these twothyratrons to cause either which is fired to extinguish the other whichis conducting current. The cathodes of both thyratrons 132 and 155 areconnected to negative line 119. Grid bias battery or other voltagesource 158 has its negative pole connected to the grid of thyratron 155and its positive pole connected to an end of secondary winding1 159 oftransformer T. The other end of this secondary winding is connected tonegative line 119.

Primary winding 160 of transformer T is connected through resistor 232and line 161 to positive line 117, and through line 162 to spring stripbrush 163, one end of which is screwed to Bakelite or other insulatingplate 164. This brush presses against the adjacent face of brass orother metal disc 165 which is integral with or electrically connectedwith metal lugs or commutator bars 166 at right angles to the plane ofdisc 165 and recessed into the periphery of Bakelite or anotherinsulating disc 167. f

This disc is concentrically and rigidly attached to shaft 168 which isrotatable in a bore through plate 164 and has an attached handle 169 onthe opposite side of plate 164. Metal disc 176 is bored so that it canrotate through a limited arc around shaft 168 and is attached to insulating arm 171 which is fastened to metal arm 172. This arm carriescontact element 173 which may attimes touch contact 174 screwed toinsulating plate 164. kSpring washer 175 is placed on shaft 168 betweendisc 170 and collar 176 which may be fastened to shaft 168 by means of aset screw. Rotation of handle 169 and shaft 168 will, therefore, rotatebars 166 and also, through friction, disc 170 and arm 172 will berotated until the arm strikes stop 177 for one direction of rotation, oruntil contact 173 strikes contact 174 for the other direction ofrotation. The degree of frictional drag can be adjusted by fasteningcollar 176 at different positions on shaft 168, thereby varying thedegree of compression of spring washer 175.

Arm 172 is connected to line 161 and so to line 117 by means of flexibleconductor 178. Contact 174 is connected to the positive terminal of bias'battery or other voltage source 179, the negative terminal of which isconnected to the grid of electronic tube 180. The cathode of this tubeis connected to negative line 119. Resistor 181 is connected between thepositive terminal of bias source 179 and line 119. The anode of tube 180is connected to one end of the double throw relay magnetizing winding182 through conductor 183. The other end of winding 182 is connected toline 117 which is also-connected to the contact arm 184 by means oftiexible conductor 185. The arm 184 is normally held in contact withcontact element 195 by a spring. Contact 195 is connected to a terminalof solenoids 96 by conductor 196 and switch 1 97.` The other terminal ofsolenoid 96 is connected to negative line 119 by conductor 188 whichisalso connected to a terminal of solenoid 86 (Figure 2). The other spacedcontact1186 of the relay is connected to the remaining terminal ofsolenoid 86 by means of conductor 187 passing through solenoidwinding217 of gear box 216. Solenoid 96 is, therefore, normallyenergized through relay contact 195, and roller 91 is accordingly pulledagainst surface 94 to allow clockwise rotation of disc 61, but not inopposite direction. Spring 84 pulls arm 57, and roller 81 abuts surface82 likewise to allow only clockwise rotation of disc 61. Then if relaywinding 182 is energized, arm 184 will be pulled against contact 186,and so solenoid 86 Will be energized, solenoid 96being de-energized.Under these conditions, spring causes roller 91 to strike surface 92,allowing only counterclockwise rotation of disc 61, and solenoid 86causes roller 81 to be pulled against surface 83, also allowing onlycounter-clockwise rotation of disc 61. The motor shaft 22, of course,rotates in a direction the reverse of the disc rotation. If power isremoved from both solenoids, the springs cause the rollers to lock disc61 against rotation in either direction. If both solenoids are to bcused, switch 197 in line 196 is closed, but if it is desired to use onlysolenoid S6, then switch 197 is opened.

Line 117 is connected to line 152 through limiting resistor 189 so thatthyratrons 132 and 155 will at all times have anode potential available,irrespective of thyratrons 137, 139, or 141. Switch 196 is connectedbetween lines 152 and 119 and is open when thyratrons 132 and 155 are inuse and switch 154 is closed. If it is' desired to cut these twothyratrons out of circuit, switch 154 is opened and switch 190'isclosed. p

The blades of double pole double throw switch 226a-226 are connected,respectively, to the positive terminal of bias source 131 and to thecathode line 119 of tube 132 and resistor 133. One switch contact 227 isconnected to conductor and is arranged to be touched by switch blade226a. When the switch is closed against contact 227, conductor 130 isconnected with the positive terminal of source 131 and with theconnected end of resistor 133, the other end of which is connected withline 119. When the switch blades are closed against contacts 228, thepositive terminal of source 131 is connected with one terminal ofsecondary winding 234 of transformer T2, and the other terminal ofwinding 234 is connected with line 119. The terminals of primary winding235 of transformer T2 are connected, respectively, with a terminal ofneon or other gaseous lamp 229 and to the junction of condenser 230 anda terminal of primary winding 160 of transformer T, the other terminalof which is connected with brush 163 by conductor 162. The remainingterminal of tube 229 is connected to one end of variable resistor 231,the other terminal of which isl connected to positive line 117 by meansof conductor 161. Resistor 232 may be connected as shown.

Switch 233 is connected between line and conductor 130 so that, byclosing switch 233, the commutating or switching action of commutator127 can be bypassed when desired. It will be seen that by opening switch233 and closing the blades of switch 226 against contacts 227, thecommutator 127 will be in circuit with thyratron 132. If, however,switch 233 is opened and the blades of switch 226a are closed againstcontact 228, commutator 127 will be elfectively out of circuit, and thetime delay circuit comprising the elements 229, 230, 231, and 232 willbe in circuit with thyratron 132.

Brushes 191, 192, and 193 are slidably mounted in slots in insulatingyblock 194 which is screwed to plate 164, and are connected,respectively, with the positive terminals of bias sources 146, 147, and148. These brushes are spaced so that any one of the commutator bars 166will, when handle 169 is turned, strike the brushes in succession,preferably after equal angular displacements `of the commutator, andthen a similar angular displacement will bring the next succeedingcommutator bar into contact with Ithe iirst brush to be struck. This istrue for either direction of rotation of the commutator. When acommutatzr bar is brought into contact with a brush, current from line117 is directed through the connected resistor 149, 150, or 151 so thatthe positive voltage developed across the resistor is sufcient toovercome the negative bias voltage, and accordingly the associatedthyratron is fired. The bias volta-ges will vary according to conditionsbut, in practice, using 105 type thyratrons, I have found that 90 to 100volts negative bias provides good quenching action when a red thyratronextinguishes another. The line voltage between conductors 117 and 119may vary from, say, 200 volts or less up to many hundreds of volts,according to conditions. The capacitance of condensers 143, 144, or 145will vary from 20 to 50 mf. each, depending upon loads, voltages, andother factors.

Arm 172 has reduced end portion-17251 which, through the resiliency ofthe arm, is forced against cam 177a which is fastened to plate 164 andhas its apex positioned so that arm 172 will be urged clockwise by thecam to force contact 173 against contact 174 in the position shown. Forthis condition, shaft 168 (Figure l) will have been turned clockwise,and the friction between disc 170 and plate 165 will force end element172a over the apex of the cam. When shaft 163 is rotated in the reversedirection, the friction causes end `element 172a to be pushed over thecam apex, and the other edge of the cam will force arm 172 against -stop177 so that the circuit including contacts 173 and 174 is broken and ismaintained open until the direction of rotation of shaft 16S isreversed.

In operation, positive line 117 is connected to the positive terminal ofa direct current generator yor other source f direct current, and line119 is connected to the negative terminal of the direct current source.The cathodes of the thyratrons, shown schematically in Figure 1, may beenergized by current from a direct current source, but it is convenientto heat these cathodes by alternating current from step-downtransformers, the cathode voltage and current depending upon the type oftube used.

First, consider that switch 154 is open and switch 19) is closed andthat the thyratrons have been heated suiiiciently to come up tooperating temperature. Then if handle 169 is turned counter-clockwise asseen in Figure 1, the commutator bars 166 will be brought into contactwith brushes 193, 192, and 191 in that order, with the result thatcurrent from line 117 and conductor 161 will pass through elements 232and 164i, brush 163, bars 166, brushes 193, 192, and 191, and thencethrough resistors 151, 150, and 149, and through switch 190 and so backto negative line 119. When this current, `of greater voltage than thatof the bias sources 148, 147, and 146, is applied to the resistors, thegrids of thyratrons 141, 139, and 137 are made positive momentarily sothat these thyratrons are tired in the order indicated. By means ofquenching condensers 144, 143, and 14S, any thyratron conducting currentis extinguished when any other one of the three is fired. If the rotorteeth 31-32 are initially overlapping the associated stator teeth 15--16by `one-third circumferential tooth width, then these rotor teeth willbe magnetically snapped into register or alignment with the stator teethwhen thyratron 141 is fired or energized, the current passing throughstator windings 55C, brush 51, slip ring 35, rotor winding 50, slip-ring 36, and out brush 53 and conductor 142 to the anode `of thyratron141, `and then through the thyratron to negative line 119. The `windings55C provide magnetic flux in the stator and rotor as indicated by thearrows, the rotor winding aiding in the establish-V ment of this flux.This spool-type rotor construction provides a short magnetic path andhigh magnet-izing force for a given current. In addition, the coil 50 issimple to wind. Either this winding or the stator wind- 10 ings could beeliminated, 'but for maximum power with minimum current, it is desirableto use both windings.

Now, when rotor teeth 31--32 are snapped into align- `ment, the rotorteeth .Z9-3G of the next motor section or phase are brought into aposition of overlapping the associated stator teeth 13-14 by one-thirdtooth width. Then, as the commutator bar 166 which previously struckbrush 193 leaves that brush and comes into contact with brush 192,thyratron 139 is fired and thyratron 141 is extinguished. When currentsuddenly passes through thyratron 139, the line 117 is connected to line119 through stator windings SSb and rotor winding 49 of the secondsection or phase, the connection being completed through brush 43, sliprings 44 and 46, brush 47, and conductor leading to the anode ofthyratron 139. T he energization of this section causes rotor teeth29-30 to snap into alignment with stator teeth 13-14 and the rotor teeth27--28 of the next phase or section are rotated to a positionoverlapping the associated stator teeth 1li-11 by one-third tooth width.Then, the same commutator bar 166 strikes brush 191 so that thyratron137 is tired and thyratron 139 is extinguished, the current passing fromline 117 through stator windings 55, brush 38, slip ring 33, rotorwinding 41, slip ring 34, brush 40, through conductor 138 to the anodeof the thyratron 137, and thence through the thyratron, then throughconductor 152 and switch 19t) to negative line 119. The current from thecathodes of the thyratron 139 and 141 likewise travels through conductor152 and switch 190 to line 119. The energization of windings 55 and 41causes rotor teeth 27-28 to snap into alignment with stator teeth 11i-11, thereby bringing rotor teeth 31-32 to a position overlapping thestator teeth 15-16 by one-third tooth width. When the next succeedingcommutator bar 166 comes into contact with brush 193, thyratron 141 isagain fired and rotor teeth 31-32 are magnetically snapped intoalignment with stator teeth 13S-16, the thyratron 137 being extinguishedthrough the agency-of condenser 145. Then the operation is repeated'asdescribed, as each commutator bar sweeps under the brushes.

lt will be seen that the successive energization of the three phases ofthe motor will cause the rotor to revolve in steps, one step movement ofthe rotor being two-thirds tooth width at the rotor circumference. Theinitial overlap of the rotor teeth will vary somewhat with load and theintensity of magnetization, but the rotor will revolve even though theinitial rotor tooth overlap varies considerably. It is assumed in theabove discussion that switch 210 in line 116 is open and that motor 10S1s not energized.

Since any thyratron discussed continues to conduct current until thenext succeeding one is red, it is obvious that the rotor is always undercontrol of a magnetic field, and therefore does not over-travel or freewheel. This is a very desirable feature, since in various servo-systemsand other applications it is quite important to be able to providedefinite motor displacements. In this case, the displacements can becontrolled accurately within a fraction of a tooth width and, by meansof suitable gearing, any desired accuracy of control can be obtained.

If thyratrons are not used and the commutator distributes currentdirectly to the windings of the motor, the width and spacing ofcommutator bars 166 and that of the brushes can be so chosen that onesection of the motor will be held magnetized until the next succeedingsection is magnetized, thereby eiiininating floating of the rotor.

if handle 169 and commutator bars 166 are rotated in reverse direction,or clockwise as seen in Figure 1, then the commutator bars 166 willstrike the brushes in the order 191, 192, and 193, and the thyratronswill be fired in the order 137, 139, and 141, and the order ofenergization of the motor will be reversed from that previouslydescribed, resulting in reverse rotation of the rotor, in steps.`Regardless of the direction of rotation '1 1 of the rotor, it moves onestep each time a commutator bar 166 comes into contact with one of thebrushes 191, 192, or 193, and the rate of rotation of the rotor and itsdirection are determined by the rate of rotation of the commutator andby its direction of rotation.

lf it is desired to count the number of commutator contacts with thebrushes, i.e. the number of step movements of the rotor, then thumbscrew202 (Figure 6) is loosened and gear 203 is swung into mesh with gear204, a mark 21011 on the commutator being initially set with respect toa fixed mark'211 on plate 16a. Thumbscrew 202 may be tightened to holdthe gears in mesh and as handle 169 is turned in, say, forwarddirection, counter 200 will register the number of steps through whichthe rotor revolves. If the handle is rotated in reverse direction, thecounter will deduct the number of steps which the rotor moves in reversedirection so that the final reading of the counter will indicate the netdifference of the number of steps forward and reverse. If it is desiredto count directly the number of steps in reverse direction, gear 209 maybe brought into mesh with gear 204i, and the reverse steps will beindicated on counter 206. Both of these counters could, of course, behoused in the same casing.

Further, a counter 212 (Figure 2) may be fastened to plate 1 of themotor with its drive gear 213 meshed with gear 64 on the motor shaft sothat the step movements of the motor shaft will be indicated. In thisway, the actual movements of the shaft are shown so that there will beno error of indicationin case a thyratron were to miss tiring for one ormore steps. Counter 212 is shown as a double type which can registerstep movements in either or both directions, and either set of numeralwheels can be cleared at any time by pushing one or both buttons 214 or215.

1f it is desired to increase the speed of the motor or the startingtorque for each step, switches 233 and 190 are opened and switch 154 isclosed. Then screws 137 (Figure 2) are loosened and block 129 is guidedby arcuate slot 136 until attached pointer 12941 is at a chosen positionwith reference to scale 130a which indicates the relative position ofbrush 128 and the stator teeth at the mo-ments of contact of commutatorbars 127 with brush 128. Since the number of these contacts perrevolution of the rotor is equal to the total number of steps of themotor, the brush 128 can be adjusted so that it will make contact with acommutator bar, regardless of phase, at the moment of one-third rotortooth overlap or at other fractional tooth overlap, as desired. Asstated before, the actual rotor tooth overlap, with respect to thestator, will vary according to load and other factors. The position ofbrush 123 may likewise be set so that the motor shows maximum speed ormaximum torque. The widths of bars 127 and brush 128 may be chosen sothat the brush contact will occur at the same relative rotor toothoverlap of the stator teeth, for either direction of rotation of therotor, or the brush can be. shifted for a change of direction ofrotation. A separate brush and commutator may be used for each phase, ifdesired.

Resistor 153 is chosen of such value that a normal or running currenttraverses the motor windings when thyratron 132 is fired and any one ofthe three thyratrons 137, 132, or is concurrently fired. The resistanceof variable resistor 156 is less than that of resistor 153 so that acurrent of increased magnitude will be passed through the motor windingswhen thyratron 155 is tired. This thyratron is red at the moment ofcontact of any commutator bar 166 with any of the brushes 191, 192, or193, since the commutator current passes through primary winding 150 oftransformer T and induces a pulse in secondary winding 159 which isphased to apply a positive pulse to the grid of thyratron 155 suicientto overcome the negative bias and so to fire it. Therefore, tube 155 isfired at the beginning of each step movement of the rotor, the tiringperiod of thyratrons varying usually from 10 to 100 microseconds.Likewise, the cle-ionization time of usual types of thyratrons variesfrom to 1,000 microseconds. When tube is tired, tube 132 is'eX-tinguished, by means of condenser 157 and associated resistors 153 and156. Resistor 153 can be variable and resistor 156 can be adjusted topass more or less starting current, as desired. Resistor 156 could belinked to a load or speed indicator or governor so that it will beautomatically varied according to load or speed of the motor.

Brush may be set so that current from line 117, line 135, brush 134,slip ring 126, and any commutator bar 127 will pass through brush 128,conductor 130, and resistor 133 to apply positive bias to the grid ofthyratron 132 to lire it when the rotor teeth overlap the stator teethby any desired amount. Switch 227-226`a will, of course, be closed underthese conditions. When tube 132 is iired, tube 155 is automaticallyextinguished and, due to higher resistance of element 153, the currentthrough the motor eld and rotor windings is reduced to a lower value.This is done since less current is required to keep the rotor movingthan is required to accelerate it from a stationary or slower speedcondition. The reduction of current for cach step of rotor rotationwill, therefore, reduce the power required as well as reduce heatingeffects. By setting brush 128, the high starting current can beautomatically reduced at any desired fractional part of a step. In otherwords, the higher current can be maintained for 10%, 30%, 50% or anydesired proportion of the step movements.

lt would be difficult to time the firing of thyratron 132 with each ofthe thyratrons 137, 139, or 141, so that simultaneous firing wouldoccur. For that reason, posi` tive line 117 is connected to conductor152 through resistor 189 which should have a sufficiently highresistance to limit the current and to provide enough potential dropacross the motor windings and connected thyratrons. The resistance ofeiement 189 can be fairly high, c llowing passage of just sufficientcurrent to cause ring ofthyratron 132 or thyratron 155, when biasedpositively. The principal current through these thyratrons passesthrough the thyratrons 137, 139, and 141-1 in sequence.

1f it is desired to use the electrical time delay circuit for ringthyratron 132, instead of commutator 127, switches 233 and 154 areclosed and switch 190 is opened, and the blades of switch 22e-22er: arebrought: into connection with contacts 228. Then, when the commutator ordistributor bars 166 are rotated, thereby periodically passing currentthrough lines 161 and 162, resistor 232, and primary 1M), thyratron 155is rst tired to pro-V vide a heavy starting current per step and thepotential drop across resistor 232 charges condenser 230 throughresistor 231 until the potential across the condenser rises to thebreakdown potential of the gas in tube 229, at which time condenser 230is suddenly discharged through primary winding 235, which is phased toprovide a positive pulse across resistor 133 of greater voltage than thenegative voltage of bias source 131. Thyratron 132 is, therefore, firedwhen tube 229 suddenly breaks down and the time delay between the ringof thyratron 155, with heavy current, and the subsequent firing ofthyratron 132 which passes less current, can be controlled by adjustingvariable resistor 231, or variable condenser 230, or both. This type ofcurrent modulator is not governed by the relative position of the rotorand stator.

When it is desired to use the booster effect of motor 108, this isconnected in circuit with lines 117 and 119 by closing switch 216 sothat the motor revolves approximately at rated speed. Then, assumingthat the shaft 22 is being rotated in steps, switch 210 is closed andthumbscrew 76 is adjusted until commutator bars 66 make contact withtriangular brush 72 (Figure 3) approximately at the moments that thethyratrons 137, 139, and 141 are fired, or slightly before, in order toallow for any effects of time lag of magnetization of clutch 101-115 orother assos/is llt components. When a bar 66 comes into contact withbrush '72., the circuit carrying current through clutchmagnetizingwinding M4 is completed from line M7, through switch Eid, brush fll,slip ring lf3, winding slip ring M2, brush lid, flexible wire 12nd,brush '72, commutator bar 6d, slip ring 63, brush 78, and throughconductor to negative H9. When winding lid is energized, magnetic iluxis caused to pass through the oil ron particle mixture between the innerface of magne ble housing element tibi and magnetizable disc 135.5attached to shaf les of motor l'iS. The magnetic held passes through aportion of this shaft and through magnet le housing element ldd. Uponestablishment of the magnetic field, the iron particles are aligned and,in effect, 'tightly bind together disc lle and element lill so thatrotor StG?, assists in driving shaft 22,. This power soest for shaft 22will serve to help accelerate shaft ZZ from zero starting speed, or froma relatively slow starting speed, and the power boost will continueuntil the bar ieuves brash 72., thereby breaking the circuit to windingThe magnetic field of the clutch then quickly colc rotating disc M iseffectively disengaged so that shaft 22 is no longer accelerated ordriven by motor tt.

The period of time during which winding iid is enermay be controlled byadjusting thumbscrew 74. if turnedy to lift brush 72., then, due to itstapered adjacent face of brush 7E: for less and less periods of time asthe brush is lifted. if thumbscrew '7d is turned in a direction to lowerbrush 72, then the periods of time of contact of the brush and thecommutator bars will be increased. Therefore, by adjusting thumbscrew74, the winding iid may be energized for a small or large fraction ofthe step movements of the rotor. Erush 72 may be of resilient characterso that it will be pressed the ends of conimutator bars tid, or a springmay be used for that purpose. 'Ehe shape of brush 72 and thecrossscctional shape of bars do can be chosen so that the winding It'will be properly energized for either direction of rotation of shaft orthumbscrew 76 can be adjusted so that block o@ and brush 7?. are swungabout guide screws 7l, against the tension of spring 77, until therotating commutator bars make contact with the brush at the propertimes. Motor lil@ can be reversed for reverse rotation of shaft or asuitable reversing gear or other mechanism 2id can joint the sections ofshaft 1%. Solenoid Elfi is connected in series with line or conductor187 and is energized when reversing relay i132 is energized. SolenoidEl?, when enereized, shifts gears, or operates a reversing clutch orother mechanism to cause the direction of rotation of shaft lfn toreverse even though motor continues to revolve in the same direction.Such reversing mechanisms are known.

The speed of rotation of shaft 106 can be chosen for optimumaccelerative or power boosting effect, as desired. The speed may beequal to or greater than the maximum speed of the step motor rotor. lfthe step motor 1s operated in such manner that the rotor comes to restat the end of each step, then a greater accelerative boost at thebeginnings of step movements will be more appropriate for maximum stepmotor speed than if the rotor is merely slowed during each step. In somecases, the speed of shaft litio could be less than the maximum speed ofthe rotor shaft 22. For very close step control, requiring the stoppingof the rotor within one step movement, it is important not to continuethe boosting effect from motor litt; long enough, during any step, tolose step control or to cause the step motor to overtravel.

The step motor is phased so that the rotor turns in counter-clockwisedirection as viewed in Figure 2 when handle 169 is turned incounter-clockwise direction as seen in Figure l, since contact 173 isseparated from contact 174, due to frictional drag on disc 176, andsolenoid 96, only, is energized. Under these conditions, rollers 31 and911 allow disc 61 to rotate in clockwise direction (Figure 2), but lockthis disc tightly against rotation in the reverse direction. This, ofcourse, allows shaftZZ and attached rotor units to rotate incounter-clockwise direction, but the rotor, through gears 6d and 62 andassociated mechanism, is prevented from rotating in clockwise direction.rThis automatic locking feature, which prevents back-swing of the rotorat any fractional position of a step displacement, is very importantsince it makes possible a smooth Working and reliable motor operationwhich, otherwise, would be very uncertain.

I have found that,l without the automatic brake, the rotor oscillates,hunts, and otherwise behaves very erratically. The cause of this is thatit is a resilient system. When the teeth of any rotor section aremagnetically snapped into alignment with the teeth of the associatedstator section, the rotor does not stop in the aligned or in-registerposition, but, due to the momentum of the rotor, continues beyond thatposition, being decelerated by the back magnetic pull until the rotorcomes to rest at the end of the step movement. Now, if the magnetizationof the next phase or section occurs at the moment of rotor stoppage, orslightly before, the teeth of the next rotor section will bemagnetically snapped forward and if the magnetization of all threephases is timed inthis manner, the motor will operate satisfactorily.If, however, the timing of the sequential energization of the phasewindings is not synchronized with the zero-speed positions of the rotor,or approximately so, then the next succeeding phase may be magnetizedwhile the rotor is rapidly moving backward as a result of reversemagnetic pull, and the reverse momentum may virtually cancel the forwardacceleration so that there is little net accelerating torque. The rotor,therefore, tends to oscillate about the aligned position, but sometimesis more or less neutralized by opposed magnetic pull and, at othertimes, is accelerated additionally while rapidly moving forward. Theresult is that no consistent rotation occurs and little power isobtainable.

The use of the locking rollers, allowing one-way rotation only,radically changes the operation of the motor, making possible continuedrotation virtually without backswing or oscillation. An important aspectof this construction is that the rotor is stopped in its most forwardposition while it is stationary and so there is little or no shock. Theactual amount of over-swing of the rotor teeth with respect to theassociated stator teeth will depend upon the load, the magnetic field,momentum, and other factors, but the brake or locking arrangement isdesigned so that rotor backswing is prevented, regardless of thefractional step position of the active rotor teeth with respect to itsassociated stator teeth. By this construction, I have found lthat thestep operation of the motor can be made to be smooth and reliable,practically without hunting or oscillations. Beyond a certain speed, thestep displacements are hardly noticeable. The same conditions apply foropposite rotation of the rotor, the brake, of course, being properlyset.

lf handle 169 is turned n clockwise direction, as seen in Figure l, thefrictional drag will cause arm tip 17211 to be quickly forced over cam177a, and contact 173 will be snapped against Contact 174, therebyapplying positive bias to the grid of tube 180 which then passes sucientcurrent through the winding 182 to cause relay contact arm 134. to bemagnetically pulled down against contact ld. This breaks the circuit tosolenoid 96 and closes the circuit, energizing solenoid 86 so thatrollers 81 and @l are set to allow counter-clockwise rotation of disc6l, but not rotation in the opposite direction. This, of course, allowsrotation of the rotor and attached shaft 2?. in clockwise direction, butnot in opposite direction. 'l he length of arm E72 is made suficient sothat contacts M3 and M4 will either be brought together, or separated,depending upon the direction of rotation of handle 169,

asada/te before the next succeeding commutator bar 166 comes intocontact with one of the brushes 19t, 192, or 193. A stepped-up gearsystem can be used. The reverse rotation of handle 169 and commutator16e-167 will reverse the order of firing of thyratrons 137, 139, and 141so that the step motor will rotate in opposite direction.

A desirable feature of the brake system is the step-up gear ratiobetween gear 62 on disc 61 and gear 6d fastened to shaft 22. Thisresults in small angular movements of shaft 22 being in effect amplifiedso that the periphery of disc 61 will, for any step movement of therotor, be displaced through a considerably greater arcuate movement thanthe corresponding arcuate peripheral displacement of the rotor.Therefore, the rotor can be locked against even small fractional stepbackswings so that more efficientA operation results. Another advantageis that the amplifying arrangement proportionally reduces the lockingforce required at the periphery of disc 61, and less bulky and ruggedconstruction can be used. More than two rollers can be used if desired,and, as stated previously, only one roller can be used. solenoid 96would not be necessary. In some applications, however, it is desirableto have the rotor automatically locked by the springs and rollers whenneither solenoid is energized.

The motor shaft may be connected with a load by means of gearing, apulley, or otherwise. Various features described in this motor may beused separately or in conjunction in order to improve the operation ofthe motor, as indicated. While the use of thyratrons is de- K scribed,it is obvious that if the commutator 16o-*167 is of heavy enoughconstruction, the thyratrons can be eliminated and the commutator can beused to distribute current directly to the motor windings. Thecommutator may be as shown or it can comprise microswitches or otherswitches or relays. The commutator may also be inthe form of a belt ortape which may be suitably driven and which may be marked, printed,punched, or equipped with capacitive, conductive, or magnetic areas inorder to modulate or distribute currents to the motor phases, asdescribed in my co-pending applications, Serial Number 295,694, tiledJune 20, 1952, Aand Serial Number 373,187, filed August l0, 1953.

What I claim is:

lt In combination, a motor having stator means, and havmg rotor meansadapted to be rotated in steps, another motor associated with said rotormeans to vary the torque of the output shaft associated therewith, meansfor effectively connecting and disconnecting the torque transmissionrelationship between said other motor and said rotor means, and meansfor synchronizing the connecting and disconnecting means with the stepsof said rotor means.

2. In combination, a motor having stator means and having rotor meansadapted to be rotated in steps, another motor associated with said rotormeans to Vary the torque of the output shaft associated therewith, meansfor effectively connecting and disconnecting the torque transmissionrelationship between said other motor and said Irotor meansintermittently, and means for synchronizlng the connecting anddisconnecting means with the steps of said rotor means.

3. In combination, a motor having stator means, and having rotor meansadapted to be rotated in steps, another motor associated with said rotormeans to vary the torque of the output shaft associated therewith, meansfor effectively connecting and disconnecting the torque transmissionrelationship between said other motor and said rotor means, and meansassociated with rotor means for making said connecting and disconnectingmeans effective or ineffective in accordance with step positions of saidrotor.

4. In combination, a motor having stator means, and having rotor meansadapted to be rotated in steps, another motor associated with said rotormeans to vary the In that case,v

16 torque of the output shaft associated therewith, variable torquetransmission means connecting said rotor means and said other motor tovary the driving relationship therebetween, and means for synchronizingthe operation of said variable torque transmission connecting means withthe steps of said rotor means.

5. In combination, a motor having stator means, and having rotor meansadapted to be rotated in steps, another motor associated with said rotormeans to vary the torque of the output shaft associated therewith, meansconnecting said rotor means and said other motor to vary the drivingrelationship therebetween, and means for maling said drivingrelationship effective substantially at the beginning of step movementsof said rotor means and for making said driving relationship ineffectiveafter predetermined displacements of said rotor means after saidbeginning of step movements.

6. In combination, a motor having stator means, and having rotor meansadapted to be rotated in steps, another motor associated with said rotormeans to vary the torque of the output shaft associated therewith, meansfor connecting said rotor means and said other motor to make effective adriving relationship therebetween, means for synchronizing effectiveaction of said connecting means with step movements of said rotor means,and means including timing means for making said connecting meansineffective after predetermined intervals after connecting said rotormeans and said other motor.

7. In combination, a motor having stator means, and having rotor meansadapted to be rotated in steps, powerdriven means associated with saidrotor means for varying the torque of the output shaft thereof,electromagnetic clutch means for connecting or disconnecting said rotormeans and said power-driven means, and commutator means driven by saidrotor means for controlling the energization of said electromagneticclutch means in synchronous relation with step movements of Said rotormeans.

8. The device as described in claim 7, said commutator means beingadjustable to vary the periods of energization of said electromagneticclutch means.

9. In an electromagnetic device, in combination, stator means andassociated rotor means, one of which has a plurality of substantiallyevenly spaced magnetizable teeth, and the other of which has a pluralityof groups of magnetizable poles, said groups of poles being positionallyphased with respect to said teeth, means for magnetizing said groups ofpoles in predetermined order, power-driven means, and means foreffectively connecting and disconnecting the torque transmissionrelationship between said powendriven means and said rotor means, andmeans for synchronizing the connecting and disconnecting means withrelative positions of said rotor means and stator means.

l0. In combination, a motor having stator means, and having rotor meansadapted to be rotated in steps, power means associated with said rotormeans to vary the torque thereof, means for connecting said rotor meansand said power means to vary the driving relationship therebetween, andmeans for making said driving relationship effective substantially atthe beginnings of step movements of said rotor means and for making saiddriving relationship substantially ineffective after predetermineddisplacements of said rotor means after said beginnings of stepmovements.

l1. In combination, a motor having stator means, and having rotor meansassociated therewith, power means associated with said rotor means tovary the torque of the output shafts thereof, means for connecting saidrotor means and said power means to make effective a drivingrelationship therebetween, and means including timing means for makingsaid connecting means substantially ineffective after predeterminedintervals after connecting said rotor means and said power means.

l2. The device of claim 5, and including means foP 17 reversing thedirection of application of torque to said rotor means by said othermotor.

13. The device of claim 5, and including means for reversing thedirection 'of application of torque to said rotor means by said othermotor, other reversing means for the step motor, and means connectingsaid reversing means and other reversing means to cause simultaneousoperation thereof.

14. The device as described in claim 5, and including means foradjusting the displacements after which said driving relationshipbecomes ineffective.

15. The device as described in claim 10, and including means foradjusting the displacements after which said p driving lrelationshipbecomes substantially ineffective.

16. In combination a motor having stator means and having rotor meansadapted to be rotated in steps, power means associated with said rotormeans to vary the torque thereof, means for connecting said rotor meansand said power means to vary the driving relationship therebetween,means for making said driving relationship eiective substantially at thebeginnings of step movements of said rotor means and for making saiddriving relationship ineffective after predetermined displacements ofsaid rotor means after said beginnings of step movements, and means forincreasing the energization 18 of said motor substantially at thebeginnings of step movements of said rotor means.

17. The device as described in claim 16 and including means for reducingthe energization of said motor before the ends of said step movements.

18. The method of operating a step motor, said method comprisingenergizing said motor intermittently to cause step movements ofthe rotorand associated power output member thereof, and applying additionalintermittent accelerative force to said power output member to increasethe stepping rate of said motor.

19. The method of operating a step motor, said method comprisingenergizing said motor intermittently to cause step movements of therotor and an associated shaft of said motor and applying additionalintermittent accelerative force to said shaft to increase the steppingrate of said motor.

20. The method of operating a step motor, said method comprisingenergizing said motor intermittently to cause step movements of therotor and an associated rotary member, and applying additionalintermittent accelerative force to said rotary member substantially vatthe beginnings of step movements thereof.

No references cited.

